Various organs and passages in the body are subject to the development of stones, calculi and the like. For example, gallstones are a common problem in the United States and are the most frequent cause of gallbladder inflammation. Calculi and concretions in other parts of the biliary system are also commonplace. Similarly, stones, calculi, concretions and the like can develop throughout the renal or urinary system, not only in the ureters and distal to them, but also in the renal tubules and in the major and minor renal calyxes.
Minimally invasive surgical procedures have been developed for the removal of stones, calculi, concretions and the like from the biliary and urinary systems, as well as for the removal or retrieval of foreign bodies from a variety of locations in the body. Such procedures avoid the performance of open surgical procedures such as, for example, a cholecystectomy. Minimally invasive procedures can instead employ percutaneous access, in which stones, calculi, concretions, foreign bodies and the like are removed through a percutaneously inserted access sheath. Several access routes are suitable, depending upon the specific system and the particular location in the system at which the stones, calculi, concretions, foreign bodies or the like are found.
Without regard to the particular access route, percutaneous extraction is often based upon the use of catheters or similar devices to engage and remove the stones, calculi, concretions, foreign bodies and the like. Such catheters and devices typically comprise a hollow, flexible sheath and a plurality of round or flat wires positioned in but extendable from the sheath. The wires are joined or arranged so as to form a means such as a basket or forceps for engaging the object to be retrieved, when the wires are extended from the sheath. The engagement means (for example, the basket) can be collapsed by withdrawing the wires into the sheath. A helical basket permits entry of the stone or the like from the side of the basket, while an open ended ("eggwhip") basket allows a head-on approach to the stone or the like. Other retrievers and graspers can include forceps or can include a loop or snare for encircling the body to be removed, the loop or snare being made of the round or flat wire.
Despite their successful use for some time, retrieval devices including round or flat wire baskets are subject to some drawbacks. It is believed, for example, that helical stone extractor baskets have never been successfully produced with flat wires, but only with round wires. Flat wires, however, have the advantage that baskets incorporating them exhibit better resistance to twisting during use. Moreover, while surgical techniques have advanced, and endoscope accessory channels of relatively smaller diameter have been developed, efforts to reduce the diameter of round wires incorporated in stone extraction baskets have unfortunately not met with similar success. In practice, the lowest useful round wire diameter (even with stainless steel wire) remains about 0.007 to 0.010 in. (about 0.178 to 0.254 mm). Because there is a significant amount of wasted space inside any sheath or cannula containing round or flat wires, this limit on useful wire diameter has prevented the development of useful helical stone extractors of small diameter, and in particular, of extractors having an outside diameter (that is, the diameter of the sheath or cannula containing the wires) below about 1.7 French (0.022 in. or 0.56 mm). The development of retrieval devices having smaller diameters than this, especially diameters below 1 French, would allow the removal of stones, calculi, concretions, foreign bodies and the like from locations deeper in the body than can be achieved with these larger, existing devices.
It should therefore be clear that it would be highly desirable to have a device for the capture and retrieval or extraction of stones, calculi, concretions, foreign bodies and the like which had an overall outside diameter significantly smaller than the outside diameter of existing retrieval or extraction devices. It would also be highly desirable for such a device to include a basket or grasper whose wires exhibited the good resistance to twisting and bending that is enjoyed by flat wires, while being capable of being formed and maintained in a helical-shape like round wires, or in a straight, flower shape like flat wires. Additionally, a portion of helical basket, or straight, flower-shaped basket wedge-shaped wires could form a grasper. It would be particularly desirable to have such a device with an outside diameter below 1 French, even as small as 0.5 French, which retained acceptable basket strength and acceptable capture and removal, extraction or retrieval properties.